1. Field of the Invention
The present invention relates to a process for preparing triazoles fused with aromatic systems by reaction of o-arylenediamines with nitrites and subsequent purification by distillation.
Triazoles fused with aromatic systems are valuable corrosion inhibitors, in particular for copper surfaces, but they can also be used as intermediates for numerous syntheses.
2. Description of the Related Art
It is already known to react o-phenylenediamine and o-diaminotoluenes in excess acetic acid with sodium nitrite (DE-OS (German Published Specification) No. 2,351,595, equivalent to U.S. Pat. Nos. 3,970,667; 3,732,239; 3,564,001). It is further known to use a lower alkyl ester of nitrous acid instead of sodium nitrite (DE-OS German Published Specification) No. 2,822,506); in this case, the reaction is carried out in an aprotic solvent, such as a hydrocarbon, or in a protic solvent, such as an alcohol or ether alcohol which can also contain small amounts of water. To initiate the diazotization and the amount of an acid, for example of a carboxylic acid, is ring closure reaction to give the triazole, a catalytic required. Instead of using a carboxylic acid as reaction initiator, the prior art reveals that acidic benzotriazole or tolytriazole have also been used (EP Nos. 62,864; 75,459).
Particular attention has always been given to the purification of the fused triazole obtained. Thus, in the process of abovementioned DE-OS (German Published Specification) No. 2,351,595, the reaction mixture, without intermediate isolation of the triazole, is made alkaline using aqueous sodium hydroxide solution and subjected several times of clarifying filtration; after the mixture has been acidified again using nitric acid, the precipitated triazole is isolated as such. In DE-OS (German Published Specification) No. 2,822,506, the reaction mixture, after distilling off volatile components, is inoculated and the triazole is recovered by crystallization. U.S. Pat. No. 3,732,239 shows that, if crude diaminotoluene is used before starting the diazotization and ring closure reaction, an expensive purification by distillation is necessary. After the reaction with aqueous sodium nitrite, the tolyltriazole is extracted from the reaction mixture which contains water and acetic acid using chloroform. After the chloroform has been distilled off, the tolyltriazole is recrystallized, for example from benzene.
However, it has also been attempted, after the diazotization with sodium nitride in a water/acetic acid reaction medium, first to separate off the benzotriazole as an oil, to wash it with water and finally to distil the benzotriazole itself under reduced pressure. Since this simple vacuum distillation was evidently not completely satisfactory, the purification of benzotriazole was refined by vacuum distillation in the presence of small amounts of formaldehyde (U.S. Pat. No. 4,170,521).
The purification by distillation apparently did not give sufficient purity and colour stability of the fused triazoles so that EP No. 75,459 additionally shows, evidently to avoid an unsatisfactory distillation, another process in which alkyl nitrites are reacted in C.sub.6 -C.sub.10 alkanols as the reaction medium and the triazole obtained is extracted from this reaction medium by means of aqueous sodium hydroxide solution.